1. Field of the Invention
This invention relates to a sensor which detects the mixing ratio of gasoline and alcohol or the like employed to as a fuel of internal combustion engine for example.
2. Description of the Prior Art
In recent years, it is planned to extract liquid alcohol from plants. The alcohol thus extracted is mixed with gasoline to use as liquid fuel for internal combustion engine. When employed in an internal combustion engine for motor vehicle, it is necessary to precisely control the mixing ratio of the liquid fuel to obtain maximum output level and avoid adverse effect upon our health due to harmful exhaust gas. This precise control is carried out each time when the liquid fuel changes. When the mixing liquid of gasoline and alcohol is put into market, it is preferably that the mixing liquid is used together with the gasoline.
For this purpose, a transparent column is provided in the condition to make its outer surface contact the mixing liquid fuel of gasoline and alcohol. Light emitting diode and photo diode are arranged to sandwich the column in its lengthwise direction, so that the light emitted from the diode enters the column and reflects at the boundary of the column and the liquid fuel to fall on the photo diode. The change of mixing ratio of the liquid causes a change of the critical angle of the light incident upon the boundary so as to affect the amount of light to which the photo diode is subjected, since the refractive index of the column against the liquid varies depending upon the change of the mixing ratio.
The light emitting diode, however, is subjected to variation according to the ambient temperature, thus it is unable to continuously obtain a precise measurement of a liquid mixing ratio unless a discrete thermal sensor is provided to compensate the output from the photo diode.
Therefore, it is an object of this invention to provide an improved sensor which is capable of continuously measuring a ratio of alcohol and gasoline with high precision irrespective of the ambient temperature in order to obtain the most appropriate timing of ignition and injection when employed to the internal combustion engine by way of example.
According to the present invention, a sensor for the mixing ratio of liquid fuel comprising; a cylindrical enclosure having both inlet and outlet opening to act as a passage through which a mixing liquid fuel flows; a transparent column concentrically disposed in the enclosure to make its outer surface contact with the liquid fuel; light emitting diode and photo diode provided so as to sandwich the column in the lengthwise direction, so that the light emitted from the former enters the column through its one end and reflects at the boundary of the column and the liquid fuel, and go out of the other end thereof to fall on the latter; a temperature compensation photo diode disposed in the enclosure with the light of the light emitting diode partly as a light source to rectify the characteristics influenced under the ambient temperature variation; a voltage control circuit provided to control the voltage across the photo diode so as to maintain uniform output from the temperature compensation photo diode.